Ever since the introduction of the microprocessor, computer systems have been getting faster and faster. In approximate accordance with Moore's law (based on Intel® Corporation co-founder Gordon Moore's 1965 publication predicting the number of transistors on integrated circuits to double every two years), the speed increase has shot upward at a fairly even rate for nearly three decades. At the same time, the size of both memory and non-volatile storage has also steadily increased, such that many of today's personal computers are more powerful than supercomputers from just 10-15 years ago. In addition, the speed of network communications has likewise seen astronomical increases.
Increases in processor speeds, memory, storage, and network bandwidth technologies have resulted in the build-out and deployment of networks with ever substantial capacities. More recently, the introduction of cloud-based services, such as those provided by Amazon (e.g., Amazon Elastic Compute Cloud (EC2) and Simple Storage Service (S3)) and Microsoft (e.g., Azure and Office 365) has resulted in additional network build-out for public network infrastructure, in addition to the deployment of massive data centers to support these services which employ private network infrastructure.
A typical data center deployment includes a large number of server racks, each housing multiple rack-mounted servers or blade servers. Communications between the rack-mounted servers is typically facilitated using the Ethernet (IEEE 802.3) protocol over copper wire cables. In addition to the option of using wire cables, blade servers and network switches and routers may be configured to support communication between blades or cards in a rack over an electrical backplane or mid-plane interconnect.
In recent years, the speed of Ethernet connections over copper wiring has reached the 10 Gigabits per second (Gpbs) and 40 Gpbs level. Moreover, The IEEE (Institute of Electrical and Electronics Engineers) is currently developing a specification (IEEE 802.3bj) defining a new backplane PHY (Physical Layer) type called 100GBASE-KR4 that is targeted for a bandwidth of 100 Gbps over electrical backplanes with a loss up to 33 dB at 7 GHz. A similar specification for a new 100 Gbps over a cable connection called 100GBASE-CR4 is also being defined by the IEEE.
An important aspect of high speed link and interconnect operation is link training During link training, a training signal pattern is transmitted from a transmit port at a first end of the link (i.e., first endpoint) to a receive port at the other (second) link endpoint. The training pattern, among other features, facilitates tuning (e.g., timing adjustments, voltage signal levels) of the link transmitter/receiver pair to account for signal noise and the like, which may lead to data errors. In a similar manner and typically concurrently, link training is also performed between a transmitter at the second link endpoint and a receiver at the first endpoint. For some high speed links, the link or interconnect comprises multiple lanes in each direction, and the training pattern is transmitted over each lane.